This blog discusses current weather, weather prediction, climate issues, and other topics

Monday, May 3, 2010

An Extraordinary May Storm

A truck was overturned by high winds near Vantage. Photo courtesy of KING-TV

The storm of the past day is really extraordinary in a number of ways:

1. A profound rainshadow over Seattle Sunday afternoon.2. Strong winds over the entire region, with some locations getting gusts of up to 60 mph. Several power outages.3. A powerful westerly surge today in the Strait of Juan deFuca with winds reaching 50-60 mph in the central and eastern Strait, with northern Whidbey Island being hit hard.4. Powerful winds in the Kittitas valley, with gusts above 50 mph.5. A strong convergence zone from Seattle to Everett, bring heavy rain and lightning.6. Heavy rains on the coast and the lower slopes of the mountains, but with heavy snow above 4000 ft, reaching 1-2 feet in some locations.7. Highly accurate forecasts of much of the above, something we could not have done ten years ago.

For warm ups, here are some high winds collected by Scott Sistek of KOMO TV:

Oak Harbor: 56 mph

Alki Beach (W. Seattle): 51 mph

Arlington: 48 mph

Everett: 47 mph

Shelton: 47 mph

Tacoma: 45 mph

Port Angeles: 41 mph

Gig Harbor: 41 mph

Olympia: 40 mph

Bellingham: 39 mph

Seattle (Sea-Tac): 39 mph

Hoquiam: 39 mph

Take a look at the maximum gusts at Smith Island, just upstream of northern Whidbey Island. Twice the gusts reached 55 knots--that's 63 mph.

Keystone Ferry runs were canceled and trees are down all over the island. The fact that many trees have leaves now makes them more vulnerable.

With all the cold and snow lately the snowpack is really doing well. Take a look at the latest plot...and remember we were down to roughly 50% of normal a few weeks ago!Now everyone is above 75%, Yakima's watershed is above 100% and the Olympics are 140%. You will be able to water your lawn this summer. It is sobering to consider that the National Weather Service's long-range (month ahead) forecast was entirely WRONG about this last few weeks...they were going for warm and dry. The skill of extended forecasts are very low.

Today we had the absolutely best convergence zone you could ask for. Look at these amazing radar and satellite images at around 1 PM. The satellite image shows the classic convergence zone line, with the zones of enhanced clearing to the north and south. One extraordinary aspect of this convergence (and you can see it in the sat picture) is that the convergence zone clouds crossed the Cascades. You don't see that very often.

Here is a high resolution MODIS image at nearly the same time. Amazing...you can see the dust storm in eastern Washington, and the Puget Sound Convergence Zone plume.

I biked home this evening and had to penetrate the convergence zone north of the UW. Lightning was flashing in front of me. I was getting wet. And I could see the clearing on the other side as I turned into my street. Just wonderful.

16 comments:

I know the central sound was in a pronounced rainshadow today, so it took away from todays events but...

We had some plowed fields E of the Mts. and they no longer exist!

We had snowflakes falling at 4pm, average high is 70. The nearest cloud in the sky was 20 miles away! It was surrreal. The sky was inverse. Bellowing clouds of snow and dust near the surface under crystal blue sky.

Rattlesnake ridge near Hanford recorded 104 mph.

I'm only 24 years old but I've never observed a day like this in May. It is boring weather here 360 days a year, but not today.

PS. You're right about the convergence zone. A friend told me it dumped snow/rain from Cashmere to past Wenatchee! That had to be from the CZ. Also, you have a wind map for the last week for Ellensburg? I'd say the last 180 hrs has averaged 20mph.

I noticed an interesting phenomenon yesterday. It was pouring from 7 to 9pm in Redmond and as I drove home through Sammamish, it was raining pretty hard on 228th street which pretty much follows the crest of the ridge.

As soon as I turned off onto Issaquah Pine Lake Rd going into SE Sammamish and slighly downhill, the road dried out even though Redmond had been soaked for at least 2 hours.

Such a small ridge creating its own rain shadow? In the midst of the convergence zone?

Here's a nexrad animation of the PSCZ yesterday from 9am to 7pm or so.

http://tinyurl.com/2f9m5lm

I could see blue sky to the north all day, and part of the day to the south, but it was cloudy with periods of rain all day here in Bothell. A late downpour brought wet snow at around 7:45pm, and then the most interesting sunset later, with a pink/orange rain curtain to the east as the sun set, almost like a reverse sunset.

Question for you: is it just me, or are these wind storms getting stronger and more frequent? Seems like since the Hannakah storm of 2006, there have been several of these magnitude storms a year, once every one or two months. My memory isn't so good, but I don't remember them so often or so severe in the 90s. Am I wrong? Thanks

Here in S.Bellingham (Fairhaven) it has been pleasant and sunny all day. Perfect gardening day! Last nights low temp was 41 so no frost. So much for thunderstorm forecasts... It was wet this morning with a little wind but cleared by 9am.

I was driving home from school at 3:30 and an Olympia radio station said there were reports of freezing rain on I-5 between exits 99 and 95..I checked my car thermometer and it said it was 55 degrees. This stretch of freeway cant be more than about 150 ft above sea level. With the heavy thunderclouds and black sky, I could sure understand if this was hail...the radio announcer said the freezing rain was building up on the freeway and there were several minor accidents.

I don't know that there are more windstorms now than earlier. Perhaps there's been more in this decade than in the 90s, but I seem to recall quite a few in the 80s, so it's quite possible it's within the range of normal variance, or there's a very long term cycle. We have to be careful about letting our limited and fallible memories guide us on things like this. Unless there's recorded data showing otherwise, I'm not ready to believe we're seeing any kind of trend.

And yes, it's quite possible to encounter freezing rain in air temps well above freezing. If the air aloft is very cold the water droplets can get supercooled (well below 32°F) without changing phase -- but they'll turn to ice as soon as they touch something that can act as a "seed" for crystallization. This is a well-known danger in aviation, where flying into clouds of such droplets can result in immediate and rapid build-up of ice on the aircraft. We don't see it much at ground level around here because we don't usually have the kind of (thunder-) storms that can bring supercooled water down from very high altitudes (and in the winter, when the water droplets nearer the ground could be supercooled, there's usually enough salt and other pollutants in the air to initiate crystallization aka "snow").

Seattle is not at all experiencing more windstorms than it has in the past. We have had two significant windstorms in the past 10 years--far less than in the 1960s, for example.

The word "windstorm" is constantly misused by the media. An actual windstorm in the Seattle area typically means gusts 58 mph or greater. Local news outlets tend to proclaim anything these days a wind storm. Apparently, 60 mph gusts in Bellingham constitutes a windstorm for Seattle. The May 3 "windstorm" did not come close to that in the Seattle area. What was extraordinary was the strength of the winds for May--that was very unusual.

In the 2000s decade, Seattle has only had 2 decent windstorms, and 3 smaller windstorms: